1. Field of the Invention
The present invention relates to a fuel gas manufacturing apparatus for manufacturing a hydrogen-rich fuel gas by modifying a hydrogen-containing fuel which contains hydrocarbon, alcohol, or the like.
2. Description of the Related Art
There has been employed in the art a hydrogen manufacturing apparatus (fuel gas manufacturing apparatus) for modifying a hydrocarbon fuel such as natural gas or the like or a hydrogen-containing fuel containing alcohol such as methanol or the like to produce a hydrogen-containing gas (modified gas) and supplying the hydrogen-containing gas as a fuel gas to a fuel cell or the like.
Such a hydrogen manufacturing apparatus basically operates to modify a hydrocarbon fuel such as an LPG (liquefied petroleum gas), a city gas, or the like with water vapor to produce a hydrogen-containing gas as a high-concentration hydrogen-rich gas, and separate high-purity hydrogen from the hydrogen-containing gas with a PSA (Pressure Swing Adsorption) device according to pressure adsorption.
Specifically, a hydrogen-containing gas produced by modifying a hydrocarbon fuel with water vapor contains various unwanted materials including CO, CO2, H2O, CH4, etc. in addition to a hydrogen gas as a major component. The PSA device has three adsorption towers, for example, each cyclically operable in adsorption, depressurization, pressure uniformization, blowing-down, and purging processes for extracting high-purity hydrogen and discharging the other components or unwanted materials as an off gas.
For example, Japanese Laid-Open Patent Publication No. 2002-20102 discloses a hydrogen manufacturing apparatus basically having, as shown in FIG. 7 of the accompanying drawings, a hydrogenerated desulfurizer 2 for being supplied with a fuel such as a city gas or the like from a compressor 1, a water-vapor modifier 3 for modifying a desulfurized fuel with water vapor to produce a high-concentration hydrogen-containing gas (hydrogen-rich gas), a catalytic combustor 4 disposed around the water-vapor modifier 3 for burning hydrogen with oxygen in air in the presence of a catalyst, a gas modifier 5 for converting carbon monoxide contained in the hydrogen-containing gas into carbon dioxide and hydrogen, and a PSA (Pressure Swing Adsorption) device 6 for separating high-purity hydrogen from the hydrogen-containing gas which has been modified by the gas modifier 5 according to pressure adsorption.
The PSA device 6 is connected to a hydrogen storage tank 8 for temporarily storing the high-purity hydrogen before it is supplied to a polymer electrolyte fuel cell (PEFC) 7, and an off-gas holder (off-gas tank) 9 for temporarily storing an off gas (unwanted materials) adsorbed from the high-purity hydrogen by the PSA device 6. The off-gas holder 9 supplies the off gas as a fuel for heating the water-vapor modifier 3 to the catalytic combustor 4.
The PSA device 6 has a plurality of adsorption towers each filled with an adsorbent for selectively adsorbing components other than hydrogen under high pressure and desorbing the adsorbed components under reduced pressure. Each of the adsorption towers cyclically operates in adsorption, desorption, replacement, and pressurization processes for extracting high-purity hydrogen and discharging other components as an off gas.
The off-gas holder 9 needs to be several times greater than the PSA device 6 for effectively performing its function, and hence the hydrogen manufacturing apparatus is of a considerably large size. In particular, the hydrogen manufacturing apparatus with the off-gas holder 9 cannot be used as a hydrogen manufacturing apparatus for household use because an installation space available therefor in households is usually small.